In a power conversion system such as a variable speed, constant frequency (VSCF) power generating system, a generator converts variable speed motive power supplied by a prime mover into variable frequency AC power. The variable frequency power is rectified and provided over a DC link to a controllable inverter. The inverter, which comprises one or more subinverters and a summing transformer, is operated to produce constant frequency AC power, which is then supplied, over a load bus, to loads requiring such power. In various applications, such as an aircraft jet engine, the size and weight of the summing transformer used in such a system is extremely important.
The physical structure of a summing transformer for use in a VSCF system such as that described above must accommodate the specific electronic system that is intended to be used. One such electronic system is a star-delta system. An example of a star-delta system that may be used in an inverter in a VSCF system may be found in Compoly et al., U.S. Pat. No. 3,775,662. The star-delta system of Compoly includes a 24-step inverter comprised of four subinverters and a summing transformer, and produces a 24-step, three-phase output. Each of the four subinverters is coupled to an associated set of three primary windings, which are carried on the summing transformer. Two of these associated sets of primary windings are connected in wye (or "star") configuration. The other two sets of of primary windings are connected in delta configuration. The three-phase output is developed through magnetic linkage of each of three selected groups of primary windings with three associated series of secondary windings also carried on the transformer. Each of the selected groups of primary windings comprises four windings, one from each of the four sets of primary windings. Each of the series of secondary windings comprises four secondary windings, each one in magnetic linkage with a different one of the associated group of primary windings. The three series of secondary windings are, in turn, connected in wye configuration.
One problem faced by those skilled in the art has been to construct a transformer capable of accommodating an electrical system of the type described in Compoly while meeting the size and weight limitations critical in typical applications, such as in an aircraft jet engine.